Refrigeration system



y 6, 1967 w. H. NEBGE N REFRIGERATION SYSTEM Filed April 5, 1966 WILLIAM H. NEBGEN INVENTOR.

J BY AGENT United States Patent f poration of Delaware Filed Apr. 5, 1966, Ser. No. 540,227 Claims. (Cl. 62-45) The present invention relates to refrigeration systems employing a sub-cooled liquid refrigerant, and provides an improved method for cooling the liquid refrigerant after it has been warmed in refrigeration service. The warm liquid refrigerant at elevated pressure is recooled by vaporizing a plurality of portions of refrigerant at successively decreasing pressure levels from the body of warm liquid refrigerant. The heat of vaporization absorbed by the vaporized refrigerant portions serves to cool the residual liquid refrigerant. The improved sequence of the present invention involves the procedure provided for re-compression of the refrigerant vapor portions, which is carried out in mechanical compression means in which the work required for compression of a refrigerant vapor portion is partially derived from vaporization of the next succeeding refrigerant vapor portion at elevated pressure into the mechanical compression means. Thus, the work required for compression of the refrigerant vapor prior to condensation and recycle is substantially reduced.

The use of sub-cooled liquid refrigerants for refrigeration service has become increasingly important in commercial service. In a conventional refrigeration cycle, the liquid refrigerant is totally vaporized during refrigeration service, and heat is absorbed as latent heat of vaporization of the refrigerant. The refrigerant vapor stream is then compressed, and the hot compressed vapor is condensed by heat exchange with ambient atmosphere, cooling water, or other ambient heat absorber. The resulting liquid refrigerant at elevated pressure and temperature is then adiabatically flashed through a valve to provide further refrigeration service.

In a cycle employing a sub-cooled liquid refrigerant, the pressure of the liquid refrigerant is not released during cooling service, and consequently only a minor or negligible proportion of vaporization takes place, and the cooling effect is primarily attained by absorption of sensible heat in the liquid refrigerant, which is consequently warmed but generally not vaporized. The cooling of the warmed liquid refrigerant prior to recycle for further refrigeration service may be attained in several ways, typical of which are the procedures described in US. Patents Nos. 2,389,106 and 3,159,008. In these prior art procedures, the warmed liquid refrigerant at elevated pressure is cooled by adibatic expansion to a lower pressure level, with concomitant flash expansion and vaporization of a portion of the liquid refrigerant at the reduced pressure. The adiabatic flash evaporation to a reduced pressure produces a cooling of the residual portion of liquid refrigerant to a low temperature level due to the absorption of heat of vaporization by the vaporized refrigerant portion. The cold residual liquid refrigerant portion is then pressurized and recycled to refrigerant service, while the vapor is compressed and condensed to liquid by heat exchange with ambient atmosphere or cooling water, and the condensed liquid refrigerant is then recycled to the adiabatic flash expansion step. This prior art procedure involving adiabatic flash expansion of liquid refrigerant in a single stage to a final reduced pressure level is essentially isenthalpic expansion and produces all of the refrigerant vapor at a uniform low pressure level, specif ically the constant equilibrium pressure level in the system after adiabatic flash expansion.

,tion into the mechanical compression means.

3,319,432 Patented May 16, 1967 In the present invention, an improved procedure is provided for the cooling of warmed liquid refrigerant employed in a sub-cooled liquid refrigeration system. The warm liquid refrigerant at elevated pressure is cooled by vaporizing a plurality of vapor portions at successively reduced pressure levels, which serves to exert a cooling effect on the residual liquid refrigerant phase. The improved sequence of the present invention involves the subsequent re-compression of the vapor portions, which is carried out in mechanical compression means in which the Work required for compression of a refrigerant vapor. portion is partially derived from vaporization of the next succeeding refrigerant vapor portion into the mechanical compression means. In other words, the vaporization is carried out in a plurality of stages at gradually diminishing pressure levels, and the vapor evolved at each pressure level performs work by exerting force or pressure in the mechanical compression means, thus aiding in the compression of a previous vapor portion and reducing the not power requirement for vapor compression. Thus, the vapor generation during liquid refrigerant cooling in the present invention is essentially isentropic, as contrasted to the isenthalpic refrigerant expansion sequence practiced in the adiabatic flash expansion procedures of the prior art. The resulting compressed vapor portions of the present invention are condensed by heat exchange with ambient atmosphere, cooling water, or other ambient heat absorber, and the resulting condensed liquid refrigerant is recycled by being subjected to further vapor evolution in accordance with the present invention. The resulting residual cold liquid refrigerant phase produced by the invention is pressurized and passed to refrigeration service as sub-cooled liquid refrigerant, which is then warmed without vaporization and is subsequently recooled in accordance with the invention.

The principal advantage of the present invention is improved efliciency in terms of reduced net power requirement for re-compression of refrigerant vapor evolved during cooling of the liquid refrigerant. This advantage is derived because the vapor evolution is essentially isentropic, with the work required for compression of a refrigerant vapor portion being partially derived from vaporization of the next succeeding refrigerant vapor por- Another advantage is that the liquid refrigerant cooling is more eflicient in terms of reduced quantity of vapor evolution to cool a unit quantity of liquid refrigerant. This advantage is attained since the refrigerant vapor portions are derived not only at successively decreasing pressure levels but also at successively decreasing temperature levels, ranging from the initial temperature of the warm liquid refrigerant to the final temperature of the cold residual liquid refrigerant. Thus, the average temperature and heat content of the vapor evolved during the cooling cycle is substantially higher, per unit quantity of vapor, than the temperature and heat content of the vapor evolved during the prior art adiabatic flash expansion of liquid refrigerant to a final low pressure level, since all of the vapor evolved in the prior art sequence is at the very low equilibrium temperature attained by the adiabatic flash expansion to low pressure. Thus, since the average heat content of the refrigerant vapor evolved during the cooling sequence of the present invention is higher than in the prior art sequence, less vapor needs to be evolved to attain a given amount of refrigerant cooling. Consequently, the size and cost of the mechanical compression means is reduced, and in addition less inventory of liquid refrigerant needs to be maintained in the system, since more of the refrigerant remains in the liquid state at the end of the cooling cycle, per unit original quantity of warm liquid refrigerant.

It is an object of the present invention to provide an improved refrigeration system.

Another object is to provide an improved refrigeration system employing a sub-cooled liquid refrigerant.

' A further object is to provide an improved method for cooling a liquid refrigerant employed as a sub-cooled l1quid refrigerant in a refrigeration system.

An additional object is to reduce the net compression power requirement for compression of refrigerant vapor evolved during cooling of a liquid refrigerant by vapor evolution, wherein the cooled liquid refrigerant is employed in a sub-cooled liquid refrigeration system.

Still another object is to provide a more efficient method for cooling a liquid refrigerant in a sub-cooled liquid refrigeration system.

Still a further object is to provide a method for cooling a liquid refrigerant for use as a sub-cooled liquid refrigerant, in which the liquid refrigerant is cooled by vapor evolution and the evolved vapor performs useful work in vapor compression.

An object is to reduce the quantity of vapor evolved during cooling of a liquid refrigerant by vapor evolution, in which the residual liquid refrigerant phase is employed in a sub-cooled liquid refrigeration system.

These and other objects and advantages of the present invention will become evident from the description which follows. Referring to the figure, a fiowsheet of a preferred embodiment of the invention is presented, involving a cyclic procedure. In the figure, valves which are closed during one part of the cyclic procedure are shown in solid black. The refrigeration cycle during which subcooled liquid refrigerant previously cooled in accordance with the invention is employed in refrigeration service will be described initially, followed by a description of the novel sequence for re-cooling liquid refrigerant involved in the present invention and illustrated in the figure.

A body of cold low pressure liquid refrigerant which has been previously cooledin accordance with the present invention is contained in vessel 1, typically at a temperature in the range of 40 C. to C. and a pressure in the range of 1.4 kg./sq. cm. to 6 kg./ sq. cm. The liquid refrigerant in the vessel 1 and elsewhere in the system may be anysuitable and reasonably volatile refrigerant, however, iammonia, propane, butane or Freon are preferred because of favorable thermodynamic and refrigeration characteristics. The term Freon employed in the present invention refers to one or a mixture of the class of halogenated hydrocarbons including Freon-ll or trichlormonofl-uormethane, Freon-12 or dichlordifiuormethane, Freon- 22 or monochlordifiuormethane and Freon-21 or dichlorfluormethane. Cold liquid refrigerant stream 2, at a low pressure typically in the range of 1.4 kg./ sq. cm. to 6 kg./ sq. cm. and temperature typically in the range of 40 C. to 0 C., passes from vessel 1 via valve 3 and flows via stream 4 and 5 to pressurizing pump 6, in which the liquid refrigerant is pressurized to an elevated pressure typically in the range of 7 kg./sq. cm. to 30 kg./sq. cm. The resultant liquid refrigerant stream 7 discharged from pump 6 is thereby sub-cooled, and is at a pressure above that at which a vapor phase can exist at the temperature of stream 7. Stream 7 now passes through refrigeration load 8, which is any desired heat exchange unit within which stream 7 provides a cooling effect by the absorption of sensible heat. Thus, the liquid refrigerant is warmed in unit 8 but is not vaporized. The resulting warmed high pressure liquid refrigerant stream 9 discharged from unit 8 is now at a temperature typically in the range of 10 C. to 100 C., and is preferably combined with condensed liquid refrigeraut stream 10 which is derived in a manner to be described infra. The combined warm liquid refrigerant stream 11 passes via stream 12, valve 13 and stream 14 into vessel 15, which thus contains a body of warm high pressure liquid refrigerant at a temperature typically in the range of 10 C. to 100 C. and pressure typically in 4 the range of 7 kg./sq. cm. to 30 kg./sq. cm. The liquid refrigerant in vessel 15 will be subsequently cooled in another part of the cycle.

The improved sequence of the present invention involves the recooling of a body of previously warm g pressure liquid refrigerant, which is shown as taking place in vessel 16. The liquid refrigerant in vessel 16 is at an elevated initial pressure typically in the range of 7 kg./ sq. cm. to 30 kg./ sq. cm. and an elevated initial temperature typically in the range of 10 C. to C., and the residual liquid refrigerant in vessel 16 after cooling is at a reduced final temperature typically in the range of 40 C. to 0 C. and reduced final pressure typically in the range of 1.4 kg./sq. cm. to 6 kg./ sq. cm. Refrigerant vapor stream 17 passes from tank 16 via valve 18, streams 19, 20 and 21, valve 22 and stream 23 into one end of vapor compression cylinder 24, within which the double acting piston 25 moves alternately in opposite linear directions. The piston 25 is driven by shaft 26, which is connected to the flywheel 27, which is rotated in a conventional manner by shaft 28 connected to motor 29. The piston 25 is shown as moving away from the point of entry of stream 23, and compressing a previously admitted portion of refrigerant vapor at the other end of cylinder 24. The resulting compressed vapor in cylinder 24, which is at a highly elevated temperature and an elevated pressure typically in the range of 7 kg./sq. cm. to 30 kg./sq. cm. passes from the end of cylinder 24 via stream 30, valve 31 and streams 32 and 33 to heat exchange condenser 34, in which the compressed refrigerant vapor is condensed to liquid by heat exchange with cooling water, ambient air, or other suitable coolant. The coolant stream 35 is admitted into unit 34 and is warmed and discharged as stream 36. The condensed high pressure liquid refrigerant is discharged from unit 34 as stream 10.

Returning now to cylinder 24, on the opposite stroke of piston 25, the valves 22 and 31 are closed and valves 37 and 38 are opened, so that the refrigerant vapor previously passed into cylinder 24 via stream 23 is compressed and recycled via stream 39, valve 38, streams 40 and 33. Further refrigerant vapor is passed into the other end of cyllnder 24 from stream 20 via stream 41, valve 37 and stream 42.

The inventive sequence of the present invention thus volves the cooling of liquid refrigerant in vessel 16 by vapor evolution at successively reduced pressure, with the evolving vapor absorbing heat from the liquid phase as heat of vaporization at successively lower temperature levels, beginning with Warm high pressure liquid refrigerant and terminating with cold low pressure residual liquid refrigerant. An important aspect of the invention is that the vapor being evolved via stream 17 from vessel 16 is employed to do useful work, in aiding in the compression of a previous vapor portion. Referring to the figure, as the p1ston 25 moves in the direction shown, it compresses vapor from an initial pressure to a final elevated pressure for discharge via stream 30. The work performed in this compression is made up of two components. One component is the work actually done by the motor 29. The other work component, which leads to the improved ethclency of the present invention, is the work done by the vapor admitted to cylinder 24 via stream 23, which prov des a pressure on the surface of the piston 25 and thus a ds p1ston 25 in moving in the direction shown and thus aids in vapor compression to form stream 30. In sum mary, the liquid refrigerant in tank 16 is cooled by vapor evolutionand the concomitant provision of latent heat of vaporization at gradually reduced pressure levels. The evolved vapor stream 17 does useful work in cylinder 24 prior to re-compression. When the piston 25 has moved completely to the end of cylinder 24 at the end of the stroke shown in the figure, cylinder 24 behind piston 25 will be filled with refrigerant vapor admitted via stream 23, at a pressure substantially the same as that in vessel 16.

A gradual reduction in the vapor pressure level within vessel 16 will take place at each stroke of piston 25, due to the cooling effect in vessel 16 attendant upon vapor evolution, until vessel 16 contains residual cold liquid refrigerant at reduced pressure. At this point, valves 18 and 13 will be closed. and valve 43 will be opened, and cooling of the warm high pressure liquid refrigerant in vessel 15 will commence via stream 44, valve 43 and streams 45 and 20. In addition, in order to provide continuity of liquid refrigerant circulation through the system, valve 3 will be closed and valves 46 and 47 will be opened. Thus, vessel 16 will supply cold liquid refrigerant to the refrigeration load 8 via stream 48, valve 46, and streams 49 and 5, while vessel 1 will receive warm high pressure refrigerant from stream 11 via streams 50 and 51, valve 47 and stream 52. A continuous sequence is thus provided, with each vessel 15, 1 and 16 alternately receiving warm high pressure liquid refrigerant via stream 11, cooling the liquid refrigerant at successively decreasing pressure levels by vapor evolution to supply stream 20 and to form residual cold low pressure liquid refrigerant, and supplying cold liquid refrigerant via stream 5. A continuous supply of refrigerant vapor via stream 20 and vapor compression in cylinder 24 in accordance with the present invention is thus also provided.

Numerous alternatives within the scope of the present invention will occur to those skilled in the art. Thus, the ranges of operating variables such as temperature and pressure enumerated supra constitute merely preferred ranges of these variables for optimum utilization of the procedural concepts of the present invention, and the procedure of the invention may also be effectively carried out in practice under conditions other than those within the ranges of operating variables enumerated supra.

The warm high pressure liquid refrigerant streams 9 and are preferably combined and passed to the body of liquid refrigerant in vessel via stream 11. However, in some instances it will be feasible or preferable to pass only stream 9 via stream 11 to vessel 15, and to pass stream 10 to a separate auxiliary vessel, not shown, for subsequent re-cooling prior to recycle. This alternative could be of some advantage in instances when streams 9 and 10 are at substantially different temperature levels.

Although the refrigerant vapor stream has been described as being compressed by the action of the double acting piston 25 in cylinder 24, other mechanical compression means may be employed for this purpose, provided that the mechanical compression means is such that the work required for compression of a refrigerant vapor portion is partially derived from vaporization of the next succeeding refrigerant vapor portion in accordance with the inventive concepts discussed supra. Thus, the mechanical compression means may consist of two in-line coaxial cylinders, each cylinder having a separate piston, with the respective pistons being connected by shaft coupling to which an external source of power such as a motor is also connected. Other power supply means besides motor 29 could be supplied in suitable instances, such as a gas turbine or steam engine.

The mechanical compression means employed to compress refrigerant vapor stream 20 may also consist of a variable speed centrifugal compressor, in which case stream 20 would continuously flow into the inlet of the centrifugal compressor as a continuous stream of vapor admitted at gradually decreasing pressure and discharged at a constant elevated pressure. In this embodiment of the invention, a driver such as a motor would be provided together with a shaft extending between the driver and the centrifugal compressor and serving to continuously rotate the compressor at variable speed. Control means would be provided to rotate the centrifugal compressor at successively increasing speed as the inlet pressure of the refrigerant vapor stream 20 derived via stream 17 from vessel 16 becomes progressively lower.

An example of an industrial application of the method of the present invention will now be described.

6 EXAMPLE The method of the present invention was applied to the cooling of a process stream from 31 C. to 4 C., by the removal of 1,000,000 B.t.u./hour. Cooling water was available at 27 C., and subcooled ammonia liquid was employed as the liquid refrigerant at 10 C. and 10.75 kg./sq. cm., with the liquid ammonia temperature rising to 27 C. in heat exchange and countercurrent to the process stream. During re-cooling of the warmed liquid ammonia, the compressed ammonia vapor was condensed at 38 C. and subcooled to 31 C. The quantity of subcooled liquid ammonia required for the refrigeration service Was 6,240 kg./hour. The cooling effect attained by ammonia vaporization was 1154 B.t.u./kg. of ammonia vaporized, and consequently the quantity of vapor produced was 1,000,000/1154 or 866 kg./hour. The net power required to compress this vapor isentropically to 14.9 kg./sq. cm. (38 C. condensing) was 28.9 theoretical horsepower.

In contrast, in a conventional refrigeration cycle for the same cooling load, an evaporator temperature of 10 C. was employed with isenthalpic fiash across the expansion valve. The quantity of ammonia vapor produced was 956 kg./hour and the not power required was 83 theoretical horsepower.

I claim:

1. A method for cooling a liquid refrigerant in a refrigeration system employing sub-cooled liquid refrigerant which comprises vaporizing a plurality of portions of refrigerant at successively decreasing pressure levels from a body of warm liquid refrigerant initially at elevated pressure, whereby residual cold liquid refrigerant is produced at reduced pressure, pressurizing said residual cold liquid refrigerant to form sub-cooled liquid refrigerant at elevated pressure, warming said sub-cooled pressurized liquid refrigerant in a heat exchange zone, to produce a refrigeration effect without vaporization of refrigerant and a first portion of recycle warm liquid refrigerant at elevated pressure, compressing said plurality of portions of refrigerant vapor to elevated pressure in mechanical compression means, wherein the work required for compression of a refrigerant vapor portion is partially derived from vaporization of the next succeeding refrigerant vapor portion into said mechanical compression means, and cooling the resulting compressed refrigerant vapor portions to condense said compressed vapor portions and thereby form a second portion of recycle warm liquid refrigerant at elevated pressure, said first and second portions of recycle warm liquid refrigerant at elevated pressure being subsequently cooled to produce further residual cold liquid refrigerant by the steps employed to cool said body of warm liquid refrigerant.

2. The method of claim 1, in which said refrigerant is selected from the group consisting of ammonia, Freon, propane and butane.

3. The method of claim 1, in which said first and second portions of recycle warm liquid refrigerant are combined, and the resulting combined recycle warm liquid refrigerant is subsequently cooled to produce further residual cold liquid refrigerant.

4. The method of claim 1, in which said mechanical compression means comprises a cylinder, said cylinder being provided with a vapor portion inlet valve and a compressed vapor outlet valve at each end, a vapor compression piston within said cylinder, a motor, said motor being provided with a flywheel, a shaft extending between said flywheel and said piston, whereby said piston is alternately driven in opposite linear directions within said cylinder, and control means to alternately pass a refrigerant vapor portion through each vapor portion inlet valve and into said cylinder, whereby a vapor portion within said cylinder is compressed by said piston through the force exerted by said shaft combined with the force exerted on said piston by the next succeeding vapor portion.

5. The method of claim 1, in which said mechanical compression means comprises a centrifugal compressor, combined with means to pass refrigerant vapor in a continuous stream from said body of warm liquid refrigerant to said centrifugal compressor, a motor, a shaft extending between said motor and said centrifugal compressor and serving to rotate said centrifugal compressor, and control means to rotate said centrifugal compressor at increasing speed as the inlet pressure of the refrigerant vapor stream derived from said body of warm liquid refrigerant is reduced.

6. A method for cooling a liquid refrigerant in a refrigeration system employing sub-cooled liquid refrigerant which comprises vaporizing a plurality of portions of refrigerant vapor at successively decreasing pressure levels from a first portion of liquid refrigerant, said first liquid refrigerant portion being warm and at elevated pressure, whereby residual cold liquid refrigerant is produced at reduced pressure from said first liquid refrigerant portion, withdrawing a cold liquid refrigerant stream from a second portion of liquid refrigerant, said second liquid refrigerant portion being cold and at reduced pressure, pressurizing said cold liquid refrigerant stream to form subcooled liquid refrigerant at elevated pressure, warming said sub-cooled pressurized liquid refrigerant in a heat exchange zone, to produce a refrigeration effect without vaporization of refrigerant and a first stream of recycle warm liquid refrigerant at elevated pressure, compressing said plurality of portions of refrigerant vapor to elevated pressure in mechanical compression means, wherein the work required for compression of a refrigerant vapor :portion is partially derived from vaporization of the next succeeding refrigerant vapor portion into said mechanical compression means, cooling the resulting compressed refrigerant vapor portions to condense said compressed vapor portions and thereby form a second stream of recycle warm liquid refrigerant at elevated pressure, combining said first and second streams of recycle warm liquid refrigerant at elevated pressure to form a third liquid refrigerant portion, said third liquid refrigerant portion being warm and at elevated pressure, and subsequently cooling said third liquid refrigerant portion to produce further residual cold liquid refrigerant by the steps employed to cool said first portion of liquid refrigerant.

7. The method of claim 6, in which said refrigerant is selected from the group consisting of ammonia, Freon, propane and butane.

8. The method of claim 6, in which said mechanical compression means comprises a cylinder, said cylinder being provided with a vapor portion inlet valve and a compressed vapor outlet valve at each end, a vapor compression piston within said cylinder, a motor, said motor being provided with a flywheel, a shaft extending between said flywheel and said piston, whereby said piston is alalternately driven in opposite linear. directions within said cylinder, and control means to alternately pass a refrigerant vapor portion through each vapor portion inlet valve and into said cylinder, whereby a vapor portion within said cylinder is compressed by said piston through the force exerted by said shaft combined with the force exerted on said piston by the next succeeding vapor portion.

9. The method of claim 6, in which said mechanical compression means comprises a centrifugal compressor, combined with means to pass refrigerant vapor in a continuous stream from said first portion of liquid refrigerant to said centrifugal compressor, a motor, a shaft extending between said motor and said centrifugal compressor and serving to rotate said centrifugal compressor, and control means to rotate said centrifugal compressor at increasing speed as the inlet pressure of the refrigerant vapor stream derived from said first portion of liquid refrigerant is reduced.

10. The method of claim 6, in which said plurality of portions of refrigerant vapor are vaporized from said first portion of liquid refrigerant at pressure levels which successively decrease from an initial pressure in the range of 7 kg./sq. cm. to 30 kg./sq. cm. to a final pressure in the range of 1.4 kg./sq. cm. to 6 kg./sq. cm., said first portion of liquid refrigerant being at an initial temperature in the range of 10 C. to C., whereby said residual cold liquid refrigerant is produced at a temperature in the range of -40 C. to 0 C., said second portion of liquid refrigerant is at a temperature in the range of 40 C. to 0 C. and pressure in the range of 1.4 kg./sq. cm. to 6 kg./ sq. cm., and said third liquid refrigerant portion is at a temperature in the range of 10 C. to 100 C. and pressure in the range of 7 kg./sq. cm. to 30 kg./sq. cm.

References Cited by the Examiner UNITED STATES PATENTS 2,750,753 6/1956 Armstrong 6253 X 3,234,746 2/1966 Cope 62-53 X FOREIGN PATENTS 1,179,345 12/1958 France.

683,153 11/1939 Germany.

LLOYD L. KING, Primary Examiner. 

1. A METHOD FOR COOLING A LIQUID REFRIGERANT IN A REFRIGERATION SYSTEM EMPLOYING SUB-COOLED LIQUID REFRIGERANT WHICH COMPRISES VAPORIZING A PLURALITY OF PORTIONS OF REFRIGERANT AT SUCCESSIVELY DECREASING PRESSURE LEVELS FROM A BODY OF WARM LIQUID REFRIGERANT INITIALLY AT ELEVATED PRESSURE, WHEREBY RESIDUAL COLD LIQUID REFRIGERANT IS PRODUCED AT REDUCED PRESSURE, PRESSURIZING SAID RESIDUAL COLD LIQUID REFRIGERANT TO FORM SUB-COOLED LIQUID REFRIGERANT AT ELEVATED PRESSURE, WARMING SAID SUB-COOLED PRESSURIZED LIQUID REFRIGERANT IN A HEAT EXCHANGE ZONE, TO PRODUCE A REFRIGERATION EFFECT WITHOUT VAPORIZATION OF REFRIGERANT AND A FIRST PORTION OF RECYCLE WARM LIQUID REFRIGERANT AT ELEVATED PRESSURE, COMPRESSING SAID PLURALITY OF PORTIONS OF REFRIGERANT VAPOR TO ELEVATED PRESSURE IN MECHANICAL COMPRESSION MEANS, WHEREIN THE WORK REQUIRED FOR COMPRESSION OF A REFRIGERANT VAPOR PORTION IS PARTIALLY DERIVED FROM VAPORIZATION OF THE NEXT SUCCEEDING REFRIGERANT VAPOR PORTION INTO SAID MECHANICAL COMPRESSION MEANS, AND COOLING THE RESULTING COMPRESSED REFRIGERANT VAPOR PORTIONS TO CONDENSE SAID COMPRESSED VAPOR PORTIONS AND THEREBY FORM A SECOND PORTION OF RECYCLE WARM LIQUID REFRIGERANT AT ELEVATED PRESSURE, SAID FIRST AND SECOND PORTIONS OF RECYCLE WARM LIQUID REFRIGERANT AT LEVATED PRESSURE BEING SUBSEQUENTLY COOLED TO PRODUCE FURTHER RESIDUAL COLD LIQUID REFRIGERANT BY THE STEPS EMPLOYED TO COOL SAID BODY OF WARM LIQUID REFRIGERANT. 